Different apparatus and methods for automatically sharpening ice skate blades are known. The most common of those systems employ counterweights to provide constant pressure of the grinding wheel against the skate blade over the full length of the blade.
The use of constant pressure alone to control the grinding of the ice skate blade in combination with grinding of the entire length of the blade can, however, cause problems. In particular, such systems tend to remove more of the metal of the blade from the end portions rather than from the center. That situation occurs because the uniform force applied by the counterweight is in a fixed direction while the skate blade typically curves upward at both ends, causing the applied force to increase along the end portions of the blade which are curved upwardly away from the grinding wheel. Examples of such machines can be found in U.S. Pat. No. 3,735,533 to Salberg and U.S. Pat. No. 3,827,185 to Smith.
U.S. Pat. No. 4,235,050 to Hannaford et al. discloses one attempt to compensate for the increased grinding at the ends of the blade by varying the force with which the grinding wheel is pressed against the blade. The grinding wheel force is varied based on the grinding resistance as sensed by measuring the power input to the motor driving the grinding wheel. That system does not, however, fully compensate for the problem of increased grinding at the distal ends of a skate blade. Furthermore, the apparatus required to practice the method is particularly complex, adding to its cost and the cost of maintenance.
U.S. Pat. No. 4,558,541 discloses yet another system for sharpening skate blades in which the blade is swung past a stationary grinding wheel. This machine relies on varying the speed with which the blade is moved past the grinding wheel to control the depth of grinding on the blade. The system varies the speed of the blade by using photodetectors which indicate the position of the blade with reference to the grinding wheel. Once the position of the blade is known, the speed of the blade relative to the grinding wheel can be increased or decreased to control the depth of grinding. That system suffers, however, from additional disadvantages, not the least of which is the complexity of the equipment which increases the cost and difficulty of maintaining the apparatus.
A brief discussion of the profiles of skate blades may be helpful for an understanding of the disadvantages of known automatic skate blade sharpening apparatus. Basically, a skate blade is constructed to have a bottom surface defining an arc of a fixed radius. A blade has a center region (a "flat") where the blade contacts the surface of the ice much of the time, and the blade is curved upward and off of the ice on either side of this region. It will be appreciated, however, that the "flat" of the blade is typically not linear, but is also curved when fully sharpened.
The radius of the blade, and therefore, the effective length of the flat, varies depending on the type of skate to which the blade is attached. A larger radius typically provides a skater with more speed, while a shorter radius provides increased maneuverability. A hockey skate typically has a radius which is approximately 9, 11 or 13 feet. A goalie skate (also for hockey) includes a substantially larger radius, typically about 28 feet. Figure skates typically have a radius of about 4 feet, and also include a notched area at the forward end of the blade for stopping. In some instances, individuals may vary the radius of any of the above designs to provide a better balance between speed and maneuverability.
In addition, it has been found that the curvature of a blade should generally be centered to balance a skater on the blade. If the curvature is modified, e.g., by filing off more of the blade at the front or back, the center of gravity for the skater may be shifted, which may strain a skater's back or knees or make skating more difficult.
All of the above systems also use counterweights to provide a force biasing the grinding wheel against the skate blade. One primary disadvantage associated with a counterweight balance grinding wheel is the tendency of the wheel to bounce or chatter on the blade, thereby forming gouges and other discontinuities to the blade. Furthermore, the counterweights typically need periodic adjustment to provide the desired level of pressure as the grinding wheel is worn away and other variables vary the weight which the counterweight is balancing against.
Moreover, many prior systems cause the grinding wheel to ride along the previous profile of a blade. Thus, these systems are not capable of correcting for defects in a blade, e.g., due to improper manual sharpening in the past or due to nicks in a blade. Once the profile of a blade is changed substantially from the manufacturer's original specifications, none of these systems is capable of returning the blade to its original profile.
Therefore, a need exists in the art for an automatic skate sharpening apparatus and method for sharpening a skate blade in such a manner that prior defects in the skate blade are corrected. Moreover, a need exists for an apparatus and method which may address the various disadvantages associated with the use of counterweights and the like.